Polymerizable type II photoinitiators and curable compositions

ABSTRACT

A polymerizable Type II photoinitiator according to Formula (I): 
     
       
         
         
             
             
         
       
         
         wherein: 
         A represents a Norrish Type II initiating group; 
         L represents a divalent linking group positioning the Norrish Type II initiating group A and the CR2R3-group in a 1-5 to a 1-8 position wherein position 1 is defined as the first atom in the aromatic or alicyclic ring of A to which L is covalently bonded and the position 5 to 8 is defined as the carbon atom of the CR2R3-group to which L is covalently bonded, with the proviso that L does not contain an amine. Radiation curable compositions and inks include the multifunctional Type II photoinitiator.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a new class of polymerizable Type IIphotoinitiators, especially suitable for food compliant radiationcurable formulations.

2. Description of the Related Art

A free radical photoinitiator is a chemical compound that initiates apolymerization of monomers when exposed to actinic radiation by theformation of a free radical. Photoinitiators are frequently used inUV-curable compositions, such as UV curable inkjet inks.

Two types of free radical photoinitiators can be distinguished. ANorrish Type I initiator is an initiator which cleaves after excitation,yielding the initiating radical immediately. A Norrish type II-initiatoris a photoinitiator which is activated by actinic radiation and formsfree radicals by hydrogen abstraction from a second compound thatbecomes the actual initiating free radical. This second compound iscalled a polymerization synergist or co-initiator.

When radiation curable compositions are used for food packaging, toysand dental applications, the amount of extractable residues is acritical issue and needs to be minimized. Low molecular weight productsare usually not completely built into the polymer network and are proneto be readily extracted or to diffuse out of the cured composition.

Especially Norrish type II initiators are a point of concern regardingextractable residues. Norrish type II photo-initiators always require aco-initiator. Aliphatic tertiary amines, aromatic amines and thiols arepreferred examples of co-initiators. After transfer of a hydrogen atomto the Norrish type II initiator, the radical generated on the synergistinitiates the polymerization. Theoretically the co-initiator is builtinto the polymer network. However, it is highly unlikely that both thehydrogen transfer and the initiation reaction yields are a hundredpercent. Side reactions are likely to occur leaving unreacted synergistand side products in the composition. In food packaging printed uponwith such a radiation curable composition, these low molecular weightresidues remain mobile and if toxic will cause health risks upon beingextracted into the food.

One approach to minimize extraction of the photoinitiator is to use aphotoinitiator having one or more ethylenically unsaturatedpolymerizable groups so that it can be copolymerized with the othermonomers of the radiation curable composition. However thecopolymerization reduces the mobility of the photoinitiator and areduction in curing speed can be observed.

JP 2004-224993 (NIPPON KAYAKU) discloses self-photopolymerization typephotopolymerization initiators used in radiation curable compositionsfor reducing its evaporation from a cured film.

Another approach in solving the extraction problem is to design NorrishType II initiators with a higher molecular weight. However by usingthese photoreactive polymers, the solution viscosity often increases toan undesirable level for a great number of applications with radiationcurable compositions, e.g. inkjet inks and lacquers.

EP 1674499 A (AGFA GRAPHICS) discloses radiation curable compositionsand photoreactive polymers including a dendritic polymer core with atleast one initiating functional group and at least one co-initiatingfunctional group. While the use of a dendritic polymer core isadvantageous for maintaining a low viscosity of the radiation curablecomposition, an improvement in curing speed is still desirable,especially in the absence of nitrogen inertisation.

Therefore, there still remains a need for photoinitiators, combining ahigh reactivity, without the need for nitrogen inertisation and a lowimpact on the viscosity of the formulation, while still maintaining alow amount of extractable residues.

SUMMARY OF THE INVENTION

According to preferred embodiments of the present invention a new classof polymerizable Type II photoinitiators is disclosed, especiallysuitable for food compliant radiation curable formulations.

According to a further preferred embodiment of the present invention,radiation curable compositions and inks including these polymerizableType II photoinitiators are disclosed.

These and other preferred embodiments of the present invention willbecome apparent in the description hereinafter.

It was surprisingly found that a polymerizable Type II photoinitiatoraccording to Formula I gave a superior curing speed and a low viscosityin radiation curable formulations while maintaining low levels ofmigratable residues. It was also observed that the polymerizable Type IIphotoinitiator according to Formula I exhibited a sufficient stabilityfor industrial applications, i.e. there was no need to store thephotoinitiator in absolute absence of light and e.g. in a CH₂Cl₂solution.

Preferred embodiments of the invention have been realised with apolymerizable photoinitiator as defined below.

Further advantages and preferred embodiments of the present inventionwill become apparent from the following description.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Definition

The term “dye”, as used in disclosing the present invention, means acolorant having a solubility of 10 mg/L or more in the medium in whichit is applied and under the ambient conditions pertaining.

The term “pigment” is defined in DIN 55943, herein incorporated byreference, as a colorant that is practically insoluble in theapplication medium under the pertaining ambient conditions, hence havinga solubility of less than 10 mg/L therein.

The term “C.I.” is used in disclosing the present application as anabbreviation for Colour Index.

The term “alkyl” means all variants possible for each number of carbonatoms in the alkyl group i.e. for three carbon atoms: n-propyl andisopropyl; for four carbon atoms: n-butyl, isobutyl and tertiary-butyl;for five carbon atoms: n-pentyl, 1,1-dimethyl-propyl, 2,2-dimethylpropyland 2-methyl-butyl etc.

Polymerizable Type II Photoinitiators

A polymerizable Type II photoinitiator according to a preferredembodiment of the present invention includes at least onephotoinitiating group, but may include 2, 3 or more photoinitiatinggroups. For example, the polymerizable Type II photoinitiator can havetwo benzophenone groups. Also different photoinitiating groups can beused in the polymerizable Type II photoinitiator, e.g. one or morebenzophenone groups and one or more thioxanthone groups. Using differentphotoinitiating groups results in an enlarged absorption spectrum forcuring. This is especially useful when colorants are used in theradiation curable compositions that absorb partly in the same spectralregion.

The polymerizable Type II photoinitiator according to Formula (I):

wherein:

-   A represents a Norrish Type II initiating group;-   L represents a divalent linking group positioning the Norrish Type    II initiating group A and the CR2R3-group in a 1-5 to a 1-8 position    wherein position 1 is defined as the first atom in the aromatic or    alicyclic ring of A to which L is covalently bonded and the position    5 to 8 is defined as the carbon atom of the CR2R3-group to which L    is covalently bonded, with the proviso that L does not contain an    amine;-   R1 represents an optionally substituted group selected from the    group consisting of an alkyl group, an alkenyl group, an alkynyl    group, an aralkyl group, an alkaryl group, an aryl group and a    heteroaryl group;-   R2 to R6 each independently represent a hydrogen or an optionally    substituted group selected from the group consisting of an alkyl    group, an alkenyl group, an alkynyl group, an aralkyl group, an    alkaryl group, an aryl group and a heteroaryl group, with the    proviso that at least one of R2 to R6 represents a hydrogen;-   any two or three groups of the group selected from R1 to R6 and L    may represent the necessary atoms to form a five to eight membered    ring; and with the proviso that at least one of L, R1 to R6 and A is    substituted with at least one ethylenically unsaturated    polymerizable group selected from the group consisting of an    acrylate group, a methacrylate group, an acrylamide group, a    methacrylamide group, a styrene group, a vinyl ether group, an allyl    ether group, an allyl ester group, a vinyl ester group, a succinate    group, a maleate group, and a maleimide group.

In a more preferred embodiment, the at least one ethylenicallyunsaturated polymerizable group in the polymerizable Type IIphotoinitiator according to Formula (I) is a group according to Formula(II):

wherein

-   X represents a functional group selected from the group consisting    of OR7, S(O)_(n)R8 and NR9R10;-   Y represents a functional group selected from the group consisting    of OR11 and NR12R13;-   R8 to R10 represent an optionally substituted group selected from    the group consisting of an alkyl group, an alkenyl group, an alkynyl    group, an aralkyl group, an alkaryl group, an aryl group and a    heteroaryl group;-   R7 and R11 to R13 represent a hydrogen or an optionally substituted    group selected from the group consisting of an alkyl group, an    alkenyl group, an alkynyl group, an aralkyl group, an alkaryl group,    an aryl group and a heteroaryl group; and-   R9 and R10 and R12 and R13 may represent the necessary atoms to form    a five to eight membered ring.

In the most preferred embodiment, the at least one ethylenicallyunsaturated polymerizable group is an acrylate group. The polymerizableType II photoinitiator may contain 2, 3 or more ethylenicallyunsaturated polymerizable groups, but preferably contains 1 or 2ethylenically unsaturated polymerizable groups, more preferably 1 or 2acrylate groups.

In a preferred embodiment, the polymerizable Type II photoinitiatorcontains only one acrylate group, since multiple acrylate groups reducethe flexibility of a cured layer.

In a preferred embodiment, the Norrish Type II initiating group A isselected from the group consisting of a substituted or unsubstitutedbenzophenone and a substituted or unsubstituted thioxanthone.

Preferred Norrish Type II initiating groups A are given below in Table1, without being limited thereto. The dotted line represents thechemical bond to the divalent linking group L.

TABLE 1

A1

A2

A3

A4

A5

A6

A7

A8

A9

A10

A11

A12

A13

In a further particularly preferred embodiment, R1 is selected from thegroup consisting of a substituted or unsubstituted alkyl group and asubstituted or unsubstituted aryl group.

In another particularly preferred embodiment R1 represents an aryl groupaccording to Formula (III):

where the dotted line represents the chemical bond to the nitrogen atomin Formula (I) and wherein E represents a group selected from the groupconsisting of an ester, an aldehyde, a ketone and an amide. An estergroup is particularly preferred.

It was found to be essential for improving curing speed that the NorrishType II initiating group A and the CR2R3-group are in a 1-5 to a 1-8position wherein position 1 is defined as the first atom in the aromaticor alicyclic ring of A to which L is covalently bonded and the position5 to 8 is defined as the carbon atom of the CR2R3-group to which L iscovalently bonded, with the proviso that L does not contain an amine.The curing speed decreased with a factor 3 to 4 when the CR2R3-group wasplaced in a 1-3 or a 1-4 position. The curing speed drops drasticallywhen the CR2R3-group is positioned further away from the Norrish Type IIinitiating group A, e.g. in a 1-10 position. In the most preferredembodiment, the CR2R3-group is positioned in a 1-5 position.

In a preferred embodiment, the divalent linking group L is representedby the group —O—(CH₂)_(n)— wherein n represents an integer selected from3 to 6.

A nitrogen atom may be present in the divalent linking group L in a formdiffering from an amine, e.g. as an amide group. This is shown below inTable 3 by the photoinitiators INI-8, INI-14, INI-15 and INI-20.

Preferred examples of polymerizable Type II photoinitiators according topreferred embodiments of the present invention are given in Table 3below without being limited thereto.

TABLE 2

INI-1

INI-2

INI-3

INI-4

INI-5

INI-6

INI-7

INI-8

INI-9

INI-10

INI-11

INI-12

INI-13

INI-14

INI-15

INI-16

INI-17

INI-18

INI-19

INI-20

INI-21

INI-22

INI-23

INI-24

INI-25

INI-26

INI-27

INI-28Radiation Curable Liquids and Inks

The radiation curable liquids and inks are preferably cured by UVradiation and are preferably radiation curable inkjet liquids or inks.The radiation curable liquids and inks can also be advantageously usedin offset printing, screen printing, flexographic printing and otherprinting or coating techniques.

The radiation curable liquids and inks are preferably non-aqueousliquids or inks. The term “non-aqueous” refers to a liquid carrier whichshould contain no water. However sometimes a small amount, generallyless than 5 wt % of water based on the total weight of the liquid orink, can be present. This water was not intentionally added but cameinto the formulation via other components as a contamination, such asfor example polar organic solvents. Higher amounts of water than 5 wt %tend to make the non-aqueous liquids and inks instable, preferably thewater content is less than 1 wt % based on the total weight of radiationcurable liquid or ink and most preferably no water at all is present.

The radiation curable liquids and inks preferably do not contain anevaporable component such as an organic solvent. But sometimes it can beadvantageous to incorporate a small amount of an organic solvent toimprove adhesion to the surface of a substrate after UV-curing. In thiscase, the added solvent can be any amount in the range that does notcause problems of solvent resistance and VOC, and preferably 0.1-10.0 wt%, and particularly preferably 0.1-5.0 wt %, each based on the totalweight of the curable liquid or ink.

The radiation curable liquids and inks are preferably part of an inkset, more preferably an inkjet ink set, including at least one inkcontaining one or more colorants, preferably one or more colourpigments. The curable ink set preferably includes at least one yellowcurable ink (Y), at least one cyan curable ink (C) and at least onemagenta curable ink (M) and preferably also at least one black curableink (K). The curable CMYK-ink set may also be extended with extra inkssuch as red, green, blue, and/or orange to further enlarge the colourgamut of the image. The CMYK-ink set may also be extended by thecombination of full density and light density inks of both colour inksand/or black inks to improve the image quality by lowered graininess.

The pigmented radiation curable ink preferably contains a dispersant,more preferably a polymeric dispersant, for dispersing the pigment. Thepigmented curable ink may contain a dispersion synergist to improve thedispersion quality and stability of the ink. Preferably, at least themagenta ink contains a dispersion synergist. A mixture of dispersionsynergists may be used to further improve dispersion stability.

The viscosity of the curable liquid and ink is preferably smaller than100 mPa·s at 30° C. and at a shear rate of 100 s⁻¹. The viscosity of theradiation curable inkjet inks and liquids is preferably smaller than 30mPa·s, more preferably lower than 15 mPa·s, and most preferably between2 and 10 mPa·s at a shear rate of 100 s⁻¹ and a jetting temperaturebetween 10 and 70° C.

The surface tension of the curable liquid and ink is preferably in therange of about 20 mN/m to about 70 mN/m at 25° C., more preferably inthe range of about 22 mN/m to about 40 mN/m at 25° C.

The curable liquid or ink may further also contain at least oneinhibitor.

The curable liquid or ink may further also contain at least onesurfactant.

Monomers and Oligomers

The polymerizable compounds used in the radiation curable liquids andinks, especially for food packaging applications, are preferablypurified compounds having no or almost no impurities, more particularlyno toxic or carcinogenic impurities. The impurities are usuallyderivative compounds obtained during synthesis of the polymerizablecompound. Sometimes, however, some compounds may be added deliberatelyto pure polymerizable compounds in harmless amounts, for example,polymerization inhibitors or stabilizers.

Any monomer or oligomer capable of free radical polymerization may beused as polymerizable compound. A combination of monomers, oligomersand/or prepolymers may also be used. The monomers, oligomers and/orprepolymers may possess different degrees of functionality, and amixture including combinations of mono-, di-, tri- and higherfunctionality monomers, oligomers and/or prepolymers may be used. Theviscosity of the radiation curable liquids and inks can be adjusted byvarying the ratio between the monomers and oligomers.

Particularly preferred monomers and oligomers are monofunctional andpolyfunctional acrylates, such as isoamyl acrylate, stearyl acrylate,lauryl acrylate, octyl acrylate, decyl acrylate, isoamylstyl acrylate,isostearyl acrylate, 2-ethylhexyl-diglycol acrylate, 2-hydroxybutylacrylate, 2-acryloyloxyethylhexahydrophthalic acid, butoxyethylacrylate, ethoxydiethylene glycol acrylate, methoxydiethylene glycolacrylate, methoxypolyethylene glycol acrylate, methoxypropylene glycolacrylate, phenoxyethyl acrylate, tetrahydrofurfuryl acrylate, isobornylacrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate,2-hydroxy-3-phenoxypropyl acrylate, vinyl ether acrylate, vinyl etherethoxy (meth)acrylate, 2-acryloyloxyethylsuccinic acid,2-acryloyxyethylphthalic acid, 2-acryloxyethyl-2-hydroxyethyl-phthalicacid, lactone modified flexible acrylate, and t-butylcyclohexylacrylate, triethylene glycol diacrylate, tetraethylene glycoldiacrylate, polyethylene glycol diacrylate, dipropylene glycoldiacrylate, tripropylene glycol diacrylate, polypropylene glycoldiacrylate, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate,1,9-nonanediol diacrylate, neopentyl glycol diacrylate,dimethylol-tricyclodecane diacrylate, bisphenol A EO (ethylene oxide)adduct diacrylate, bisphenol A PO (propylene oxide) adduct diacrylate,hydroxypivalate neopentyl glycol diacrylate, propoxylated neopentylglycol diacrylate, alkoxylated dimethyloltricyclodecane diacrylate andpolytetramethylene glycol diacrylate, trimethylolpropane triacrylate, EOmodified trimethylolpropane triacrylate, tri (propylene glycol)triacrylate, caprolactone modified trimethylolpropane triacrylate,pentaerythritol triacrylate, pentaerithritol tetraacrylate,pentaerythritolethoxy tetraacrylate, dipentaerythritol hexaacrylate,ditrimethylolpropane tetraacrylate, glycerinpropoxy triacrylate, andcaprolactam modified dipentaerythritol hexaacrylate, or an N-vinylamidesuch as, N-vinylcaprolactam or N-vinylformamide; or acrylamide or asubstituted acrylamide, such as acryloylmorpholine.

Other suitable monofunctional acrylates include caprolactone acrylate,cyclic trimethylolpropane formal acrylate, ethoxylated nonyl phenolacrylate, isodecyl acrylate, isooctyl acrylate, octyldecyl acrylate,alkoxylated phenol acrylate, tridecyl acrylate and alkoxylatedcyclohexanone dimethanol acrylate.

Other suitable difunctional acrylates include alkoxylated cyclohexanonedimethanol diacrylate, alkoxylated hexanediol diacrylate, dioxane glycoldiacrylate, dioxane glycol diacrylate, cyclohexanone dimethanoldiacrylate, diethylene glycol diacrylate and neopentyl glycoldiacrylate.

Other suitable trifunctional acrylates include propoxylated glycerinetriacrylate and propoxylated trimethylolpropane triacrylate.

Other higher functional acrylates include di-trimethylolpropanetetraacrylate, dipentaerythritol pentaacrylate, ethoxylatedpentaerythritol tetraacrylate, methoxylated glycol acrylates andacrylate esters.

Furthermore, methacrylates corresponding to the above-mentionedacrylates may be used with these acrylates. Of the methacrylates,methoxypolyethylene glycol methacrylate, methoxytriethylene glycolmethacrylate, hydroxyethyl methacrylate, phenoxyethyl methacrylate,cyclohexyl methacrylate, tetraethylene glycol dimethacrylate, andpolyethylene glycol dimethacrylate are preferred due to their relativelyhigh curing speed and higher adhesion to an ink-receiver surface.

Furthermore, the inkjet inks may also contain polymerizable oligomers.Examples of these polymerizable oligomers include epoxy acrylates,aliphatic urethane acrylates, aromatic urethane acrylates, polyesteracrylates, and straight-chained acrylic oligomers.

Suitable examples of styrene compounds are styrene, p-methylstyrene,p-methoxystyrene, β-methylstyrene, p-methyl-β-methylstyrene,α-methylstyrene and p-methoxy-β-methylstyrene.

Suitable examples of vinylnaphthalene compounds are 1-vinylnaphthalene,α-methyl-1-vinylnaphthalene, β-methyl-1-vinylnaphthalene,4-methyl-1-vinylnaphthalene and 4-methoxy-1-vinylnaphthalene.

Suitable examples of N-vinyl compounds are N-vinylcarbazole,N-vinylpyrrolidone, N-vinylindole, N-vinylpyrrole, N-vinylphenothiazine,N-vinylacetoanilide, N-vinylethylacetoamide, N-vinylsuccinimide,N-vinylphthalimide, N-vinylcaprolactam and N-vinylimidazole.

Examples of vinyl ethers having at least one vinyl ether group includeethyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, octadecylvinyl ether, cyclohexyl vinyl ether, butanediol divinyl ether, hydroxylbutyl vinyl ether, cyclohexane dimethanol monovinyl ether, phenyl vinylether, p-methylphenyl vinyl ether, p-methoxyphenyl vinyl ether,α-methylphenyl vinyl ether, β-methylisobutyl vinyl ether andβ-chloroisobutyl vinyl ether, diethyleneglycol divinyl ether,triethylene glycol divinyl ether, n-propyl vinyl ether, isopropyl vinylether, dodecyl vinyl ether, diethylene glycol monovinyl ether,cyclohexanedimethanol divinyl ether, 4-(vinyloxy)butyl benzoate,bis[4-(vinyl oxy)butyl]adipate, bis[4-(vinyl oxy)butyl]succinate,4-(vinyloxy methyl)cyclohexylmethyl benzoate,bis[4-(vinyloxy)butyl]isophthalate,bis[4-(vinyloxymethyl)cyclohexylmethyl]glutarate,tris[4-(vinyloxy)butyl]trimellitate, 4-(vinyloxy)butyl steatite,bis[4-(vinyloxy)butyl]hexanediylbiscarbamate,bis[4-(vinyloxy)methyl]cyclohexyl]methyl]terephthalate,bis[4-(vinyloxy)methyl]cyclohexyl]methyl]isophthalate,bis[4-(vinyloxy)butyl](4-methyl-1,3-phenylene)-biscarbamate,bis[4-vinyloxy)butyl] (methylenedi-4,1-phenylene)biscarbamate and3-amino-1-propanol vinyl ether.

A preferred class of monomers and oligomers are vinyl ether acrylatessuch as those described in U.S. Pat. No. 6,310,115 (AGFA), incorporatedherein by reference. Particularly preferred compounds are2-(2-vinyloxyethoxy)ethyl (meth)acrylate, most preferably the compoundis 2-(2-vinyloxyethoxy)ethyl acrylate.

Inhibitors

The radiation curable liquids and inks may contain a polymerizationinhibitor. Suitable polymerization inhibitors include phenol typeantioxidants, hindered amine light stabilizers, phosphor typeantioxidants, hydroquinone monomethyl ether commonly used in(meth)acrylate monomers, and hydroquinone, t-butylcatechol, pyrogallol,2,6-di-tert.butyl-4-methylphenol may also be used.

Suitable commercial inhibitors are, for example, SUMILIZER™ GA-80,SUMILIZER™ GM and SUMILIZER™ GS produced by Sumitomo Chemical Co. Ltd.;GENORAD™ 16, GENORAD™ 18 and GENORAD™ 20 from Rahn AG; IRGASTAB™ UV10and IRGASTAB™ UV22, TINUVIN™ 460 and CGS20 from Ciba SpecialtyChemicals; FLOORSTAB™ UV range (UV-1, UV-2, UV-5 and UV-8) fromKromachem Ltd, ADDITOL™ S range (S100, S110, S120 and S130) from CytecSurface Specialties.

The inhibitor is preferably a polymerizable inhibitor.

Since excessive addition of these polymerization inhibitors may lowerthe curing speed, it is preferred that the amount capable of preventingpolymerization is determined prior to blending. The amount of apolymerization inhibitor is preferably lower than 5 wt %, morepreferably lower than 3 wt % of the total ink or liquid.

Surfactants

The radiation curable liquids and inks may contain a surfactant. Thesurfactant(s) can be anionic, cationic, non-ionic, or zwitter-ionic andare usually added in a total quantity less than 20 wt % based on thetotal weight of the radiation curable liquids or ink and particularly ina total less than 10 wt % based on the total weight of the radiationcurable liquid or ink.

Suitable surfactants include fluorinated surfactants, fatty acid salts,ester salts of a higher alcohol, alkylbenzene sulphonate salts,sulphosuccinate ester salts and phosphate ester salts of a higheralcohol (for example, sodium dodecylbenzenesulphonate and sodiumdioctylsulphosuccinate), ethylene oxide adducts of a higher alcohol,ethylene oxide adducts of an alkylphenol, ethylene oxide adducts of apolyhydric alcohol fatty acid ester, and acetylene glycol and ethyleneoxide adducts thereof (for example, polyoxyethylene nonylphenyl ether,and SURFYNOL™ 104, 104H, 440, 465 and TG available from AIR PRODUCTS &CHEMICALS INC.).

For non-aqueous radiation curable liquids and ink preferred surfactantsare selected from fluoro surfactants (such as fluorinated hydrocarbons)and silicone surfactants. The silicones are typically siloxanes and canbe alkoxylated, polyether modified, polyether modified hydroxyfunctional, amine modified, epoxy modified and other modifications orcombinations thereof. Preferred siloxanes are polymeric, for examplepolydimethylsiloxanes.

In the radiation curable liquids or ink a fluorinated or siliconecompound may be used as a surfactant, however, a cross-linkablesurfactant would be preferred. It is therefore preferred to use acopolymerizable monomer having surface-active effects, for example,polyacrylate copolymers, silicone modified acrylates, silicone modifiedmethacrylates, acrylated siloxanes, polyether modified acrylic modifiedsiloxanes, fluorinated acrylates, and fluorinated methacrylates; theseacrylates can be mono-, di-, tri- or higher functional (meth)acrylates.

Surfactants are known for use in the radiation curable liquids and inksto reduce the surface tension of the liquid or ink and to reduce thecontact angle on the substrate, i.e. to improve the wetting of thesubstrate by the ink. On the other hand, the jettable fluid must meetstringent performance criteria in order to be adequately jettable withhigh precision, reliability and during an extended period of time. Toachieve both wetting of the substrate by the ink and high jettingperformance, typically, the surface tension of the ink is reduced by theaddition of one or more surfactants. In the case of curable inkjet inks,however, the surface tension of the inkjet ink is not only determined bythe amount and type of surfactant, but also by the polymerizablecompounds, the polymeric dispersants and other additives in the inkcomposition.

Depending upon the application a surfactant can be used with a high, lowor intermediate dynamic surface tension. Silicone surfactants aregenerally known to have low dynamic surface tensions while fluorinatedsurfactants are known to have higher dynamic surface tensions.

Useful commercially available fluorinated surfactants are for examplethe ZONYL™ range of fluoro-surfactants from DUPONT and the FLUORAD™range of fluoro-surfactants from 3M.

Silicone surfactants are often preferred, especially the reactivesilicone surfactants, which are able to be polymerized together with thepolymerizable compounds during the curing step.

Useful commercially available silicone surfactants are oftenpolysiloxane surfactants, especially polyether modified polysiloxanes,preferably with one or more acrylate function in order to becomepolymerizable.

Examples of useful commercial silicone surfactants are those supplied byBYK CHEMIE GMBH (including BYK™-302, 307, 310, 331, 333, 341, 345, 346,347, 348, UV3500, UV3510 and UV3530), those supplied by TEGO CHEMIESERVICE (including TEGO RAD™ 2100, 2200N, 2250, 2300, 2500, 2600 and2700), EBECRYL™ 350 a polysilixone diacrylate and EBECRYL™ 1360 apolysiloxane hexaacrylate from CYTEC INDUSTRIES BV and EFKA™-3000 series(including EFKA™-3232 and EFKA™-3883) from EFKA CHEMICALS B.V.

Colorants

Colorants used in the radiation curable inks may be dyes, pigments or acombination thereof. Organic and/or inorganic pigments may be used. Thecolorant is preferably a pigment or a polymeric dye, most preferably apigment.

The pigments may be black, white, cyan, magenta, yellow, red, orange,violet, blue, green, brown, mixtures thereof, and the like. This colourpigment may be chosen from those disclosed by HERBST, Willy, et al.Industrial Organic Pigments, Production, Properties, Applications. 3rdedition. Wiley-VCH, 2004. ISBN 3527305769.

Particular preferred pigments are:

-   -   C.I. Pigment Yellow 1, 3, 10, 12, 13, 14, 17, 55, 65, 73, 74,        75, 83, 93, 97, 109, 111, 120, 128, 138, 139, 150, 151, 154,        155, 175, 180, 181, 185, 194 and 213.    -   C.I. Pigment Red 17, 22, 23, 41, 48:1, 48:2, 49:1, 49:2, 52:1,        57:1, 81:1, 81:3, 88, 112, 122, 144, 146, 149, 169, 170, 175,        176, 184, 185, 188, 202, 206, 207, 210, 216, 221, 248, 251, 254,        255, 264, 266, 270 and 272.    -   C.I. Pigment Violet 1, 2, 19, 23, 32, 37 and 39.    -   C.I. Pigment Blue 15:1, 15:2, 15:3, 15:4, 15:6, 16, 56, 61 and        (bridged) aluminium phthalocyanine pigments.    -   C.I. Pigment Orange 5, 13, 16, 34, 40, 43, 59, 66, 67, 69, 71        and 73.    -   C.I. Pigment Green 7 and 36.    -   C.I. Pigment Brown 6 and 7.

Suitable pigments include mixed crystals of the above particularpreferred pigments. Mixed crystals are also referred to as solidsolutions. For example, under certain conditions different quinacridonesmix with each other to form solid solutions, which are quite differentfrom both physical mixtures of the compounds and from the compoundsthemselves. In a solid solution, the molecules of the components enterinto the same crystal lattice, usually, but not always, that of one ofthe components. The x-ray diffraction pattern of the resultingcrystalline solid is characteristic of that solid and can be clearlydifferentiated from the pattern of a physical mixture of the samecomponents in the same proportion. In such physical mixtures, the x-raypattern of each of the components can be distinguished, and thedisappearance of many of these lines is one of the criteria of theformation of solid solutions. A commercially available example isCinquasia Magenta RT-355-D from Ciba Specialty Chemicals.

Carbon black is preferred as a black pigment. Suitable black pigmentsinclude carbon blacks such as Pigment Black 7 (e.g. Carbon Black MA8™from MITSUBISHI CHEMICAL), REGAL™ 400R, MOGUL™ L, ELFTEX™ 320 from CABOTCo., or Carbon Black FW18, Special Black 250, Special Black 350, SpecialBlack 550, PRINTEX™ 25, PRINTEX™ 35, PRINTEX™ 55, PRINTEX™ 90, PRINTEX™150T from DEGUSSA. Additional examples of suitable pigments aredisclosed in U.S. Pat. No. 5,389,133 (XEROX).

It is also possible to make mixtures of pigments. For example, in someapplications a neutral black ink is preferred and can be obtained e.g.by mixing a black pigment and a cyan pigment into the ink. Also pigmentsmay be combined to enlarge the colour gamut of an ink set. Theapplication may also require one or more spot colours. Silver and goldare often desired colours for making a product more attractive by givingit an exclusive appearance.

Also non-organic pigments may be present in the inks. Suitable pigmentsare C.I. Pigment Metal 1, 2 and 3. Illustrative examples of theinorganic pigments include titanium oxide, barium sulphate, calciumcarbonate, zinc oxide, lead sulphate, yellow lead, zinc yellow, red ironoxide (III), cadmium red, ultramarine blue, prussian blue, chromiumoxide green, cobalt green, amber, titanium black and synthetic ironblack. However, care should be taken to prevent migration and extractionof heavy metals in food application. In the preferred embodiment nopigments are used which contain a heavy metal selected from the groupconsisting of arsenic, lead, mercury and cadmium.

Pigment particles in inkjet ink should be sufficiently small to permitfree flow of the ink through the inkjet-printing device, especially atthe ejecting nozzles. It is also desirable to use small particles formaximum colour strength and to slow down sedimentation.

The numeric average pigment particle size is preferably between 0.050and 1 μm, more preferably between 0.070 and 0.300 μm and particularlypreferably between 0.080 and 0.200 μm. Most preferably, the numericaverage pigment particle size is no larger than 0.150 μm. An averageparticle size smaller than 0.050 μm is less desirable for decreasedlight-fastness, but mainly also because very small pigment particles orindividual pigment molecules thereof may still be extracted in foodpackaging applications.

The numeric average pigment particle size of pigment particles is bestdetermined with a Brookhaven Instruments Particle Sizer BI90plus basedupon the principle of dynamic light scattering. The ink is then diluted,for example, with ethyl acetate to a pigment concentration of 0.002 wt%. The measurement settings of the BI90plus are: 5 runs at 23° C., angleof 90°, wavelength of 635 nm and graphics=correction function.

In the case of a white curable ink, preferably a pigment with arefractive index greater than 1.60, preferably greater than 2.00, morepreferably greater than 2.50 and most preferably greater than 2.60 isused. The white pigments may be employed singly or in combination.

Preferably titanium dioxide is used for the pigment with a refractiveindex greater than 1.60. Titanium oxide occurs in the crystalline formsof anatase type, rutile type and brookite type. The anatase type has arelatively low density and is easily ground into fine particles, whilethe rutile type has a relatively high refractive index, exhibiting ahigh covering power. Either one of these is usable in this invention. Itis preferred to make the most possible use of characteristics and tomake selections according to the use thereof. The use of the anatasetype having a low density and a small particle size can achieve superiordispersion stability, ink storage stability and ejectability. At leasttwo different crystalline forms may be used in combination. The combineduse of the anatase type and the rutile type which exhibits a highcoloring power can reduce the total amount of titanium oxide, leading toimproved storage stability and ejection performance of ink.

For surface treatment of the titanium oxide, an aqueous treatment or agas phase treatment is applied, and an alumina-silica treating agent isusually employed. Untreated-, alumina treated- or alumina-silicatreated-titanium oxide are employable.

The numeric average particle diameter of the titanium oxide or otherwhite pigments is preferably from 50 to 500 nm, more preferably from 150to 400 nm, and most preferably from 200 to 350 nm. Sufficient hidingpower cannot be obtained when the average diameter is less than 50 nm,and the storage ability and the jet-out suitability of the ink tend tobe degraded when the average diameter exceeds 500 nm. The determinationof the numeric average particle diameter is best performed by photoncorrelation spectroscopy at a wavelength of 633 nm with a 4 mW HeNelaser on a diluted sample of the pigmented inkjet ink. A suitableparticle size analyzer used was a MALVERN™ nano-S available fromGoffin-Meyvis. A sample can be, for example, be prepared by addition ofone drop of ink to a cuvet containing 1.5 mL ethyl acetate and mixeduntil a homogenous sample was obtained. The measured particle size isthe average value of 3 consecutive measurements consisting of 6 runs of20 seconds.

Generally pigments are stabilized in the dispersion medium by dispersingagents, such as polymeric dispersants or surfactants. However, thesurface of the pigments can be modified to obtain so-called“self-dispersible” or “self-dispersing” pigments, i.e. pigments that aredispersible in the dispersion medium without dispersants.

The pigment is preferably used in a pigment dispersion used forpreparing inks in an amount of 10 to 40 wt %, more preferably of 15 to30 wt % based on the total weight of the pigment dispersion. In acurable inkjet ink the pigment is preferably present in an amount of 0.1to 20 wt %, preferably 1 to 10 wt % based on the total weight of theinkjet ink.

Dispersants

The dispersant is preferably a polymeric dispersant.

Typical polymeric dispersants are copolymers of two monomers but maycontain three, four, five or even more monomers. The properties ofpolymeric dispersants depend on both the nature of the monomers andtheir distribution in the polymer. Suitable copolymeric dispersants havethe following polymer compositions:

-   -   statistically polymerized monomers (e.g. monomers A and B        polymerized into ABBAABAB);    -   alternating polymerized monomers (e.g. monomers A and B        polymerized into ABABABAB);    -   gradient (tapered) polymerized monomers (e.g. monomers A and B        polymerized into AAABAABBABBB);    -   block copolymers (e.g. monomers A and B polymerized into        AAAAABBBBBB) wherein the block length of each of the blocks (2,        3, 4, 5 or even more) is important for the dispersion capability        of the polymeric dispersant;    -   graft copolymers (graft copolymers consist of a polymeric        backbone with polymeric side chains attached to the backbone);        and    -   mixed forms of these polymers, e.g. blocky gradient copolymers.

Suitable polymeric dispersants are listed in the section on polymericdispersants in EP 1790696 A (AGFA) incorporated herein as a specificreference.

The polymeric dispersant has preferably a polymerization degree DPbetween 5 and 1000, more preferably between 10 and 500 and mostpreferably between 10 and 100.

The polymeric dispersant has preferably a number average molecularweight Mn between 500 and 30000, more preferably between 1500 and 10000.

The polymeric dispersant has preferably a weight average molecularweight Mw smaller than 100000, more preferably smaller than 50000 andmost preferably smaller than 30000.

The polymeric dispersant has preferably a polydispersity PD smaller than2, more preferably smaller than 1.75 and most preferably smaller than1.5.

Commercial examples of polymeric dispersants are the following:

-   -   DISPERBYK™ dispersants available from BYK CHEMIE GMBH;    -   SOLSPERSE™ dispersants available from NOVEON;    -   TEGO™ DISPERS™ dispersants from DEGUSSA;    -   EDAPLAN™ dispersants from MUNZING CHEMIE;    -   ETHACRYL™ dispersants from LYONDELL;    -   GANEX™ dispersants from ISP;    -   DISPEX™ and EFKA™ dispersants from CIBA SPECIALTY CHEMICALS INC;    -   DISPONER™ dispersants from DEUCHEM; and    -   JONCRYL™ dispersants from JOHNSON POLYMER.

Particularly preferred polymeric dispersants include SOLSPERSE™dispersants from NOVEON, EFKA™ dispersants from CIBA SPECIALTY CHEMICALSINC and DISPERBYK™ dispersants from BYK CHEMIE GMBH.

Particularly preferred dispersants for UV-curable pigmented dispersionsare SOLSPERSE™ 32000, 35000 and 39000 dispersants from NOVEON.

The polymeric dispersant is preferably used in an amount of 2 to 600 wt%, more preferably 5 to 200 wt % based on the weight of the pigment.

Preparation of Radiation Curable Inks

The average particle size and distribution is an important feature forinkjet inks. The ink may be prepared by precipitating or milling thepigment in the dispersion medium in the presence of the dispersant.

Mixing apparatuses may include a pressure kneader, an open kneader, aplanetary mixer, a dissolver, and a Dalton Universal Mixer. Suitablemilling and dispersion apparatuses are a ball mill, a pearl mill, acolloid mill, a high-speed disperser, double rollers, a bead mill, apaint conditioner, and triple rollers. The dispersions may also beprepared using ultrasonic energy.

Many different types of materials may be used as milling media, such asglasses, ceramics, metals, and plastics.

In a preferred embodiment, the grinding media can include particles,preferably substantially spherical in shape, e.g. beads consistingessentially of a polymeric resin or yttrium stabilized zirconium oxidebeads.

In the process of mixing, milling and dispersion, each process isperformed with cooling to prevent build up of heat, and for radiationcurable inks as much as possible under light conditions in which actinicradiation has been substantially excluded.

The ink may contain more than one pigment, the ink may be prepared usingseparate dispersions for each pigment, or alternatively several pigmentsmay be mixed and co-milled in preparing the dispersion.

The dispersion process can be carried out in a continuous, batch orsemi-batch mode.

The preferred amounts and ratios of the ingredients of the mill grindwill vary widely depending upon the specific materials and the intendedapplications. The contents of the milling mixture include the mill grindand the milling media. The mill grind includes pigment, polymericdispersant and a liquid carrier. For inkjet inks, the pigment is usuallypresent in the mill grind at 1 to 50 wt %, excluding the milling media.The weight ratio of pigment over polymeric dispersant is 20:1 to 1:2.

The milling time can vary widely and depends upon the pigment, selectedmechanical device and residence conditions, the initial and desiredfinal particle size, etc. In a preferred embodiment of the presentinvention pigment dispersions with an average particle size of less than100 nm may be prepared.

After milling is completed, the milling media is separated from themilled particulate product (in either a dry or liquid dispersion form)using conventional separation techniques, such as by filtration, sievingthrough a mesh screen, and the like. Often the sieve is built into themill, e.g. for a bead mill. The milled pigment concentrate is preferablyseparated from the milling media by filtration.

In general it is desirable to make the inks in the form of aconcentrated mill grind, which is subsequently diluted to theappropriate concentration for use in the printing system. This techniquepermits preparation of a greater quantity of pigmented ink from theequipment. By dilution, the ink is adjusted to the desired viscosity,surface tension, colour, hue, saturation density, and print areacoverage for the particular application.

Inkjet Printing Methods

The inkjet printing method according to a preferred embodiment of thepresent invention includes the steps of:

-   a) providing a radiation curable composition according to a    preferred embodiment of the present invention; and-   b) at least partially curing the radiation curable composition.

In a preferred embodiment of the inkjet printing method according to thepresent invention, the radiation curable composition is applied to asubstrate by inkjet printing or by flexographic printing. For example,the radiation curable composition is applied as a primer on a substrateby flexographic printing and at least partially cured, and then asolvent inkjet ink or radiation curable inkjet ink is printed on the atleast partially cured primer.

In one embodiment of the inkjet printing method, the applied layer is awhite primer, preferably containing a titanium dioxide pigment. Whiteprimers can be advantageously used, for example, on transparentsubstrates to enhance the contrast and the vividness of colour inks.White curable inks are then either used for so-called “surface printing”or “backing printing” to form a reflection image on a transparentsubstrate. In surface printing, a white background is formed on atransparent substrate using a white ink and further thereon, a colorimage is printed, where after the formed final image is viewed from theprinted face. In so-called backing printing, a color image is formed ona transparent substrate using color inks and then a white ink is appliedonto the color inks, and the final formed image is observed through thetransparent substrate. In a preferred embodiment a colour inkjet ink isjetted on partially cured white inkjet ink. If the white ink is onlypartially cured, an improved wettability of the colour ink on the whiteink layer is observed. Partially curing immobilizes the ink on thesubstrate surface. A quick test to verify that the white inkjet ink ispartially cured can be done by rubbing a finger or a cloth across theprinted surface, whereby it is observed that ink can be smeared orsmudged on the surface.

In another preferred embodiment of the inkjet printing method, theapplied layer is a colourless layer. This layer can be present as aprimer, for example, for improving the adhesion of the image, or as anoutermost layer, for example, for improving the glossiness of the image.

The above layers are preferably applied by a printing technique selectedfrom the group consisting of inkjet printing, flexographic printing,offset printing and screen printing.

Alternatively, above layers are applied by a coating technique selectedfrom the group consisting of dip coating, knife coating, extrusioncoating, spin coating, slide hopper coating and curtain coating.

Inkjet Printing Device

Curable liquids and inks according to preferred embodiments of thepresent invention may be jetted by one or more print heads ejectingsmall droplets of ink in a controlled manner through nozzles onto anink-receiver surface, which is moving relative to the print head(s).

A preferred print head for the inkjet printing system is a piezoelectrichead. Piezoelectric inkjet printing is based on the movement of apiezoelectric ceramic transducer when a voltage is applied thereto. Theapplication of a voltage changes the shape of the piezoelectric ceramictransducer in the print head creating a void, which is then filled withink. When the voltage is again removed, the ceramic expands to itsoriginal shape, ejecting a drop of ink from the print head. However theinkjet printing method according to the present invention is notrestricted to piezoelectric inkjet printing. Other inkjet print headscan be used and include various types, such as a continuous type andthermal, electrostatic and acoustic drop on demand type.

At high printing speeds, the inks must be ejected readily from the printheads, which puts a number of constraints on the physical properties ofthe ink, e.g. a low viscosity at the jetting temperature, which may varyfrom 25° C. to 110° C., a surface energy such that the print head nozzlecan form the necessary small droplets, a homogenous ink capable of rapidconversion to a dry printed area, . . . .

The inkjet print head normally scans back and forth in a transversaldirection across the moving ink-receiver surface. Often the inkjet printhead does not print on the way back. Bi-directional printing ispreferred for obtaining a high areal throughput. Another preferredprinting method is by a “single pass printing process”, which can beperformed by using page wide inkjet print heads or multiple staggeredinkjet print heads which cover the entire width of the ink-receiversurface. In a single pass printing process the inkjet print headsusually remain stationary and the ink-receiver surface is transportedunder the inkjet print heads.

Curing Device

Curable liquids and inks according to preferred embodiments of thepresent invention can be cured by exposing them to actinic radiation,preferably by ultraviolet radiation.

The curing device may be arranged in combination with the print head ofthe inkjet printer, travelling therewith so that the curable liquid isexposed to curing radiation very shortly after been jetted.

In such an arrangement it can be difficult to provide a small enoughradiation source connected to and travelling with the print head.Therefore, a static fixed radiation source may be employed, e.g. asource of curing UV-light, connected to the radiation source by means offlexible radiation conductors such as a fibre optic bundle or aninternally reflective flexible tube.

Alternatively, the actinic radiation may be supplied from a fixed sourceto the radiation head by an arrangement of mirrors including a mirrorupon the radiation head.

The source of radiation arranged not to move with the print head, mayalso be an elongated radiation source extending transversely across theink-receiver surface to be cured and adjacent the transverse path of theprint head so that the subsequent rows of images formed by the printhead are passed, stepwise or continually, beneath that radiation source.

Any ultraviolet light source, as long as part of the emitted light canbe absorbed by the photo-initiator or photo-initiator system, may beemployed as a radiation source, such as, a high or low pressure mercurylamp, a cold cathode tube, a black light, an ultraviolet LED, anultraviolet laser, and a flash light. Of these, the preferred source isone exhibiting a relatively long wavelength UV-contribution having adominant wavelength of 300-400 nm. Specifically, a UV-A light source ispreferred due to the reduced light scattering therewith resulting inmore efficient interior curing.

UV radiation is generally classed as UV-A, UV-B, and UV-C as follows:

-   -   UV-A: 400 nm to 320 nm    -   UV-B: 320 nm to 290 nm    -   UV-C: 290 nm to 100 nm.

Furthermore, it is possible to cure the image using, consecutively orsimultaneously, two light sources of differing wavelength orilluminance. For example, the first UV-source can be selected to be richin UV-C, in particular in the range of 260 nm-200 nm. The secondUV-source can then be rich in UV-A, e.g. a gallium-doped lamp, or adifferent lamp high in both UV-A and UV-B. The use of two UV-sources hasbeen found to have advantages e.g. a fast curing speed and a high curingdegree.

For facilitating curing, the inkjet printer often includes one or moreoxygen depletion units. The oxygen depletion units place a blanket ofnitrogen or other relatively inert gas (e.g. CO₂), with adjustableposition and adjustable inert gas concentration, in order to reduce theoxygen concentration in the curing environment. Residual oxygen levelsare usually maintained as low as 200 ppm, but are generally in the rangeof 200 ppm to 1200 ppm.

EXAMPLES

Materials

All materials used in the following examples were readily available fromstandard sources such as Aldrich Chemical Co. (Belgium) and Acros(Belgium) unless otherwise specified. The water used was deionizedwater.

DPGDA is dipropyleneglycoldiacrylate from SARTOMER.

-   VEEA is 2-(vinylethoxy)ethyl acrylate, a difunctional monomer    available from NIPPON SHOKUBAI, Japan.-   TMPTA is trimethylolpropane triacrylate available as SARTOMER™-   SR351 from SARTOMER.-   M600 is dipentaerythritol hexaacrylate and an abbreviation for-   MIRAMER™ M600 available from RAHN AG.-   2-Hydroxythioxanthen-9-one was prepared according to the example 1    of GB 2108487 (SERICOL).-   4-(piperazin-1-yl)-benzoic acid ethyl ester was supplied by Chess    Fine Organics.-   IRGACURE™ 127 is    2-hydroxy-1-{4-[4-(2-hydroxy-2-methyl-propionyl)-benzyl]-phenyl}-2-methyl-propan-1-one,    a photoinitiator available from CIBA SPECIALTY CHEMICALS.-   COMPINI-1 is a comparative initiator which was prepared according to    Top et al., Journal of Organometallic Chemistry 643-644, 350-356    (2002).

COMPINI-2 is a comparative initiator represented by the followingformula:

-   COMPINI-2 was synthesized as follows:

(4-benzoylphenoxy)-acetic acid was prepared according to Chen et al.,Macromolecular Chemistry and Physics (2007), 208(15), 1694-1706. 25.6 g(0.10 mol) (4-benzoylphenoxy)-acetic acid was dissolved in 100 mLtoluene and 30 mL dimethyl acetamide. 14.8 g (0.20 mol) sec. butanol and28 g (0.15 mol) p.-toluene sulfonic acid were added. The reactionmixture was refluxed under azeotropical removal of water. 250 mL ethylacetate was added and the mixture was extracted with 200 mL 1 N NaOH.The organic fraction was dried over MgSO₄ and the solvent was removedunder reduced pressure. COMPINI-2 was isolated as a white crystallinecompound. 29.8 g (95%) of COMPINI-2 was isolated.

COMPCOINI-1 is a comparative co-initiator represented by the followingformula:

COMPCOINI-1 was synthesized as follows:

7.53 g (40 mmol) of 2-(2-ethoxyethoxy)ethyl acrylate was heated to 50°C. 2.93 g (40 mmol) diethyl amine was added dropwise and the reactionwas allowed to continue for four hours at 50° C. An additional 0.145 g(2 mmol) diethyl amine was added and the reaction was allowed tocontinue for an additional three hours at 50° C. The reaction mixturewas allowed to cool down to room temperature. GC analysis revealed acomplete conversion of the acrylate. COMPCOINI-1 was used withoutfurther purification.

TEGO™ Rad 2100 is a silicone polyether acrylate surfactant availablefrom DEGUSSA.

-   Surfactant A is a solution of 1 wt % TEGO™ Rad 2100 in VEEA. SPECIAL    BLACK™ 550 is a carbon black pigment with a BET of 110 m²/g    available from DEGUSSA.-   HOSTAPERM™ Blue P-BFS is a cyan pigment (C.I. Pigment Blue 15:4)    available from CLARIANT.-   CINQUASIA™ Magenta RT-355-D is a quinacridone pigment from CIBA    SPECIALTY CHEMICALS.-   PY150 is an abbreviation used for Yellow Pigment E4GN-GT, a C.I.    Pigment Yellow 150 pigment from LANXESS.-   GENORAD™ 16 is a polymerization inhibitor from RAHN AG.-   S35000 is an abbreviation for SOLSPERSE™ 35000, a    polyethyleneimine-polyester hyperdispersant from NOVEON.-   PET100 is a 100 μm unsubbed PET substrate with on the backside an    antiblocking layer with antistatic properties available from    AGFA-GEVAERT as P100C PLAIN/ABAS.-   Measurement-   1. TDE-Level

The TDE-level represents the amount of volatile extractables by thermaldesorption. The amount of volatile extractables is determined on fullycured coatings by direct thermal desorption method, i.e. without samplepreparation. The fully cured coating on a PET100 substrate having abacking layer was analysed with a GERSTEL™ TDS2 ThermoDesorption Systemfrom Gerstel Gmbh & Co. KG using as operation conditions: 1.54 cm² ofthe cured coating was analyzed during 10 minutes at 150° C. with on-lineGC evaluation of peak intensity for the desorbed components. The ovenprogram was set to 40° C. for 30 seconds, followed by a temperatureincrease at a rate of 15° C./minute until 300° C., and keeping thesample at 300° C. for 5 minutes. The chromatographic column was a Db1column from J&W (30m×0.32 mm, 1 mm film thickness); the carrier gas wasHe at a flow rate of 2 mL/min. The desorbed compounds were trapped onTenaxTA at −60° C.

The back coating on the PET100 substrate contained volatile compounds,including NMP. The amount of NMP detected was used as an internalstandard to calculate the amount of volatile compounds from the curedcoating expressed in ppm (mg extractable compound per g of curableliquid). The amount of volatile compounds of the cured coating isobtained by subtraction of the amount of volatile compounds of thePET100 substrate from the total amount of volatile compounds of curedcoating and PET100 substrate. This amount is very much depending uponthe composition of the curable liquid. The evaluation scale used for theexamples is given by Table 3.

TABLE 3 Total amount of desorbed components from the cured coatingEvaluation >5,000 ppm bad >3,000 ppm poor 1,000-3,000 ppm acceptable<1,000 ppm good <500 ppm very good

-   2. Curing Degree

The curing degree is tested on a coating immediately after curing withUV light. The cured coating is rubbed with the means of a Qtip. When thesurface is not damaged, the coating is fully cured. When some of thecured coating can be damaged, the coating is only partly cured. When thewhole cured coating is damaged, the coating is not cured.

-   3. Curing Speed

The curing speed was defined as the percentage of the maximum output ofthe lamp needed to cure the samples. The lower the number the highercuring speed. A sample was considered as fully cured at the momentscratching with a Q-tip caused no visual damage.

A percentage of more then 100% of the maximum output of the lamp meansthat the speed of the conveyer belt had to be reduced to get the samplefully cured at the maximum output of the lamp. The higher thepercentage, the more the belt had to be slowed down. A curing speed of160% means a belt speed of 12.5 m/min at the maximum output of the lamp.A percentage between 150% and 200% is considered as at the edge ofpractical use. A percentage above 200% is considered out of the rangefor practical use and no higher percentages are measured.

-   4. Viscosity

The viscosity of the formulations was measured using a BrookfieldDV-II+viscometer at 25° C. at 3 rotations per minute (RPM) using a CPE40 spindle. A viscosity of less than 50 mPa·s was regarded to besuitable for inkjet printing.

Example 1

This example illustrates the synthesis of several polymerizablephotoinitiators according to a preferred embodiment of the presentinvention.

The synthesis of INI-1

Synthesis of 4-[(3-methylamino)propoxy]benzophenone

253.7 g (1.27 mol) 4-hydroxybenzophenone was dissolved in 2.56 l2-butanone. 884.5 g (6.3 mol) potassium carbonate and 201.5 g (1.27 mol)1-bromo-3-chloro-propane were added. The mixture was refluxed for 16hours. The mixture was allowed to cool down to room temperature and theinorganic salts were removed by filtration. The solvent was removedunder reduced pressure. The residue was treated with 250 mL acetone and600 mL isopropyl acetate. The residue partially solidified. The solventwas removed and the residue was treated with 1.5 L water. The crude4-(3-chloropropoxy)benzophenone crystallized from the medium, wasisolated by filtration and dried. 228 g of the crude4-(3-chloropropoxy)benzophenone was isolated.

109.9 g (0.4 mol) of the crude 4-(3-chloropropoxy)benzophenone wasdissolved in 550 mL acetonitrile. 310 g (4 mol) of a 40% solution ofmethyl amine in water was added and the mixture was heated to 60° C. for2 hours. The undissolved residue in the reaction mixture was removed byfiltration and an additional 155 g (2 mol) of a 40% solution of methylamine in water was added. The reaction was allowed to continue for 4hours at 60° C. The reaction was allowed to cool down to roomtemperature and the solvent was removed under reduced pressure. Theresidue was dissolved in 1 L water and the pH was adjusted to 1.4 usinga 6N HCl-solution. The mixture was stirred for 2 hours at 40° C. and theprecipitated product was isolated by filtration. The residue was treatedwith 500 mL methylene chloride, isolated by filtration and dried. Thehydrochloric acid salt was dissolved in 500 mL water and the pH wasadjusted to 12 using a 10 N NaOH solution. The mixture was extractedwith 500 mL methylene chloride. The organic fraction was dried overMgSO₄ and the solvent was removed under reduced pressure. The oilyresidue crystallized upon standing. 60 g (56%) of4-[(3-methylamino)propoxy]benzophenone was isolated.

Synthesis of Photoinitiator INI-1

30 g (0.15 mol) 2-hydroxy-3-methacryloyloxypropyl acrylate, 1.83 g (15mmol) 4-dimethylamino-pyridine and 1.5 g BHT were dissolved in 200 mLacetone. 20.9 mL (0.15 mol) triethyl amine was added at roomtemperature. 34.6 g (0.23 mol) methacrylic anhydride was added drop wiseover 30 minutes and the reaction was allowed to continue at roomtemperature for one hour. The solvent was removed under reduced pressureand 2,3-di-methacryloyloxypropyl acrylate was purified by preparativecolumn chromatography on Prochrom LC 80 column, using Kromasil Si 60A 10mm as silica and a gradient elution from methylene chloride to methylenechloride/methanol 95/5 at a flow rate of 150 mL per minute. 21.3 g (50%)of 2,3-di-methacryloyloxypropyl acrylate was isolated.

2.5 g (9.2 mmol) 4-[(3-methylamino)propoxy]benzophenone was dissolved in20 mL acetonitrile. 2.6 g (9.2 mmol) 2,3-di-methacryloyloxypropylacrylate and 0.2 g BHT were added and the mixture was heated to reflux.The reaction was allowed to continue for 18 hours at reflux. Thereaction mixture was allowed to cool down to room temperature and theundissolved residual 4-[(3-methylamino)propoxy]benzophenone was removedby filtration. The solvent was evaporated under reduced pressure and theobtained INI-1 was used without further purification. The molar ratio ofINI-1 on excess 2,3-di-methacryloyloxypropyl acrylate was 3 to 1, based¹H-NMR analysis. INI-1 was used without further purification.

The Synthesis of INI-2 to INI-4 Synthesis of4-[(3-alkylamino)propoxy]benzophenones

25 g (91 mmol) 4-(3-chloropropoxy)benzophenone was dissolved in 300 mLacetonitrile. 82 g (1.26 mol) of a 70% of ethyl amine solution in waterwas added and the reaction mixture was heated to 70° C. The reaction wasallowed to continue for 16 hours at 70° C. The solvent was evaporatedunder reduced pressure and the residue was treated with 100 mL water.The mixture was acidified to pH=1 and the precipitated products wereisolated by filtration. The precipitated product was treated with amixture of 200 mL ethyl acetate and 500 mL water. The aqueous fractionwas isolated and the pH was adjusted to 12 using a 5 N NaOH solution.The mixture was extracted twice with 200 mL ethyl acetate. The organicfraction was dried over MgSO₄ and the solvent was evaporated underreduced pressure. 12.5 g of 4-[(3-ethylamino)propoxy]benzophenone wasisolated.

R=Bu

10 g (36 mmol) 4-(3-chloropropoxy)benzophenone was dissolved in 100 mLacetonitrile. 26.3 g (0.36 mol) n.-butyl amine was added and the mixturewas heated to 70° C. for 30 hours. The solvent was evaporated underreduced pressure and the residue was treated with 500 mL water. The pHwas adjusted to pH=1. The mixture was stirred for one hour at 40° C. Themixture was cooled to 10° C. and the precipitated compounds wereisolated by filtration. The precipitate was treated with 200 mL waterand the pH was adjusted to 12, using a 1 N NaOH-solution. The mixturewas extracted with 200 mL methylene chloride. The organic fraction wasdried over MgSO₄ and evaporated under reduced pressure. The crude

4-[(3-butylamino)propoxy]benzophenone was purified by preparative columnchromatography on a SVP D40 Merck-Np column, using a gradient elutionfrom methylene chloride to methanol at a flow rate of 40 mL per minute.4.4 g of 4-[(3-butylamino)propoxy]benzophenone was isolated.

R═C₆H₁₃

10 g (36 mmol) 4-(3-chloropropoxy)benzophenone was dissolved in 100 mLacetonitrile. 36.4 g (0.36 mol) n.-hexyl amine was added and the mixturewas heated to 70° C. for 20 hours. The solvent was evaporated underreduced pressure. The oily residue was treated with 500 mL water. Themixture was acidified to pH=1 and stirred for 16 hours at roomtemperature. The precipitated compounds were isolated by filtration andwashed with 200 mL 1 N HCl. The precipitate was treated with 200 mL 1 NNaOH. The mixture was extracted with 200 mL methylene chloride. Theorganic fraction was dried over MgSO₄ and the solvent was evaporatedunder reduced pressure. The crude 4-[(3-hexylamino)propoxy]benzophenonewas purified by preparative column chromatography on a Prochrom LC80column, using Kromasil Si 60A 10 mm as silica and a gradient elutionfrom methylene chloride to methylene chloride/methanol 68/32 at a flowrate of 150 mL per minute. 3.9 g of4-[(3-hexylamino)propoxy]benzophenone was isolated.

Synthesis of INI-2 to INI-4:

7 mmol of the appropriate benzophenone was dissolved in 10 mLethylacetate. 80 mg BHT and 1.2 g (3.5 mmol) pentaerythritoltetraacrylate were added and the reaction mixture was refluxed for 20hours. The solvent was removed under reduced pressure and the initiatormixture was used without further purification. The mixtures werecharacterized using LC-MS. The results are summarized in Table 3. Theratios are determined from the relative peak intensities.

TABLE 4 INI-2 INI-3 INI-4 R = R = R = Compound Et Bu Hex

18.5 19.3 25.5

2.75 not de- tec- ted not de- tec- ted

4.75 not de- tec- ted not de- tec- ted

13 12.5 14

13.9 16.5 17.2

26.5 34.4 3.3

26 17.3 13The Synthesis of INI-5:

10.6 g (30 mmol) pentaerythritol tetra-acrylate and 70 mg BHT weredissolved in 20 mL ethyl acetate. The mixture was heated to 70° C. and16.2 g (60 mmol) 4-[(3-methylamino)propoxy]benzophenone was added. Thereaction was allowed to continue at room temperature for 24 hours. Thesolvent was removed under reduced pressure and the crude mixture wasdirectly used for evaluation in radiation curable formulations. Theacrylate/benzophenone/hydroxyl-ratio was determined by ¹H-NMRspectroscopy to be 31/46/23.The synthesis of INI-6:

30 g (0.13 mol) 2-hydroxythioxanthen-9-one was suspended in 350 mLacetone. 61.6 g (0.39 mol) 1-bromo-3-chloro-propane and 62.8 g (0.46mol) potassium carbonate were added. The mixture was refluxed for 6hours. The mixture was allowed to cool down to room temperature. Theprecipitated salts were removed by filtration and the solvent wasevaporated under reduced pressure. The residue was suspended in amixture of 300 mL ethyl acetate and 200 mL water. The precipitatedresidue was isolated by filtration and redissolved in a mixture of 100mL methylene chloride and 50 mL water. Both the ethyl acetate fractionand methylene chloride fraction were isolated, pooled and dried overMgSO₄. The solvent was removed under reduced pressure and2-(3-chloropropoxy)-9H-thioxanthen-9-one was purified by preparativecolumn chromatography on a Merck SVP D40 column, using a gradientelution from methylene chloride/hexane 30/70 to methylenechloride/hexane 50/50 at a flow rate of 40 mL per minute. 26.5 g of2-(3-chloropropoxy)-9H-thioxanthen-9-one was isolated.

26 g (85 mmol) 2-(3-chloropropoxy)-9H-thioxanthen-9-one is suspended in140 mL acetonitrile. 66 g (73.2 mL, 0.85 mol) of a 40% solution ofmethyl amine in water was added and the mixture was heated to 60° C.After four hours, 1.3 g (8.5 mmol) sodium iodide and 20 mL of a 40%solution of methyl amine in water were added and the reaction wasallowed to continue for 16 hours at 60° C. The precipitated compoundswere isolated by filtration and washed three times with 100 mLacetonitrile. The pooled acetonitrile fractions were evaporated underreduced pressure. The crude 2-(3-methylaminopropoxy)thioxanthen-9-onewas crystallized from 200 mL hexane, isolated by filtration and dried.19 g of 2-(3-methylaminopropoxy)thioxanthen-9-one was isolated.2-(3-methylaminopropoxy)thioxanthen-9-one was further purified bypreparative column chromatography on a Prochrom LC80 column, usingKromasil C18 100A 10 mm as silica and methanol/1M ammonium acetate 68/32as eluent at a flow rate of 150 mL per minute.

5 g (14 mmol). 2-(3-methylaminopropoxy)thioxanthen-9-one was dissolvedin 60 mL ethanol. 2.5 g (7 mmol) pentaerythritol tetraacrylate in 20 mLmethylene chloride was added and the mixture was refluxed for 20 hours.The solvent was removed under reduced pressure and the residual oil wasdried under vacuum. INI-5 was used as mixture of compounds. Theacrylate/benzophenone/hydroxyl-ratio was determined by ¹H-NMRspectroscopy to be 2/1/0.7.

The synthesis of INI-9:

21.5 g (79 mmol) 4-(3-chloropropoxy)benzophenone was dissolved in 150 mLacetonitrile. The mixture was heated to reflux and 38.5 mL (0.39 mol)3-(methylamino)-1-propanol was added. The reaction was allowed tocontinue for 20 hours at reflux. The mixture was allowed to cool down toroom temperature and the solvent was removed under reduced pressure. Theresidue was dissolved in 150 mL t.butyl methyl ether. The organic layerwas extracted with 200 mL 0.1 N hydrochloric acid. The aqueous layer wasremoved. The organic layer was extracted three times with 100 mL 0.1 Nhydrochloric acid. The three aqueous fractions were pooled and the pHwas adjusted to 12, using a 5 N NaOH solution. The alkaline solution wasextracted with 200 mL t.butyl methyl ether. The organic fraction wasdried over MgSO₄ and evaporated under reduced pressure. 17.5 g of thecrude intermediate was isolated.

9 g (27 mmol) of the intermediate was dissolved in 100 mL methylenechloride. 6.4 mL (46 mmol) triethyl amine was added, followed by thedrop wise addition of 5.8 g (46 mmol) 3-chloropropionyl chloride, whilethe temperature was kept below by 35° C. The reaction was allowed tocontinue for one hour at room temperature. 0.5 g BHT and 7.5 mL (54mmol) triethyl amine were added. The reaction was allowed to continuefor one hour at room temperature. The reaction mixture was evaporatedunder reduced pressure. The residue was dissolved in 150 mL ethylacetate and extracted with 150 mL water. The organic fraction was driedover MgSO₄ and evaporated under reduced pressure. The crude INI-9 waspurified by preparative column chromatography on a Merck SVP D40 column,using a gradient elution from 100% methylene chloride over 100% ethylacetate to ethyl acetate/methanol 98/2 at a flow rate of 50 mL perminute. 1.43 g (14%) of INI-9 was isolated as a yellow oil.

The synthesis of INI-10:

25 g (90 mmol) 4-(3-chloropropoxy)benzophenone and 41 g (0.46 mol)2-(ethylamino)-ethanol were dissolved in 200 mL acetonitrile. Thereaction mixture was heated to 70° C. and the reaction was allowed tocontinue for 72 hours. The reaction mixture was allowed to cool down toroom temperature and the solvent was evaporated under reduced pressure.The residue was dissolved in 200 mL t.butyl methyl ether. The organicfraction was extracted with 200 mL 0.1 N hydrochloric acid. The aqueousfraction was removed. The organic fraction was extracted three timeswith 150 mL 0.1 N hydrochloric acid. The three aqueous fractions werepooled and the pH was adjusted to 12, using a 5 N NaOH solution. Themixture was extracted twice with 100 mL t.butyl methyl ether. The pooledorganic fractions were dried over MgSO₄ and evaporated under reducedpressure. 25.9 g (89.3%) of the intermediate was isolated.

5 g (15 mmol) of the intermediate was dissolved in 60 mL methylenechloride. 2.1 mL (15 mmol) triethyl amine was added, followed by thedrop wise addition of 1.5 mL (15 mmol) 3-chloroproionyl chloride, whilethe temperature rose to 15° C. The reaction was allowed to continue forone hour at room temperature. An additional 1.1 mL (7.5 mmol) triethylamine and 0.75 mL (0.75 mmol) 3-chloropropionyl chloride were added andthe reaction was allowed to continue for an additional hour at roomtemperature. An additional 4.2 mL (30 mmol) triethyl amine was added andthe reaction was allowed to continue for an addition hour at roomtemperature. The reaction mixture was extracted twice with 50 mL 0.1 Nhydrochloric acid. 0.3 g BHT was added to the organic fraction. Theorganic fraction was dried over MgSO₄ and evaporated under reducedpressure. The crude INI-10 was purified by preparative columnchromatography on a Merck SVP D40 column, using a gradient elution from100% methylene chloride to 100% methanol over 30 minutes at a flow rateof 40 mL per minute. 3.3 g (58%) of INI-10 was isolated as a yellow oil.

The synthesis of INI-11:

41 g (0.55 mol) 2-(methylamino)-ethanol and 25 g (90 mmol)4-(3-chloropropoxy)benzophenone were dissolved in 200 mL acetonitrile.The reaction mixture was heated to 70° C. and the reaction was allowedto continue for 24 hours at 70° C. The reaction mixture was allowed tocool down to room temperature and the solvent was evaporated underreduced pressure. The residue was dissolved in 200 mL methylene chlorideand extracted with 200 mL 5 times with 100 mL 1 N hydrochloric acid. Theaqueous fractions were pooled and the pH was adjusted to 12 with 2 NNaOH. The aqueous layer was extracted twice with 200 mL methylenechloride. The pooled organic fractions were dried over MgSO₄ and thesolvent was evaporated under reduced pressure. 23.7 g (84.5%) of theintermediate was isolated.

4.7 g (15 mmol) of the intermediate was dissolved in 60 mL methylenechloride and 2.1 mL (15 mmol) triethyl amine was added, followed by adropwise addition of 1.5 mL (15 mmol) 3-chloropropionyl chloride. Thereaction was allowed to continue for one hour at room temperature. Anadditional 4.2 mL (30 mmol) triethyl amine was added and the reactionwas allowed to continue for one hour at room temperature. The reactionmixture was extracted twice with 50 mL 0.1 N hydrochloric acid. 0.3 gBHT was added to the organic fraction. The organic fraction was driedover MgSO₄ and the solvent was removed under reduced pressure. The crudeINI-11 was purified by preparative column chromatography on a ProchromLC80 column, using Kromasil C18 100 Å 10 μm as silica and MeOH/waterbuffered at pH 4.2, using triethyl amine/acetic acid as buffer, aseluent. The pure fractions were evaporated under reduced pressure untilall methanol was removed. 250 mL methylene chloride was added and the pHof the aqueous fraction was adjusted to 10, using 5 N NaOH. The organicfraction was dried over MgSO₄ and evaporated under reduced pressure. 0.6g (11%) of INI-11 was isolated as a yellow oil.

The synthesis of INI-12:

8 g (26 mmol) 2-(3-chloropropoxy)-9H-thioxanthen-9-one was dissolved in80 mL acetonitrile. The mixture was heated to reflux and 13.2 mL (130mmol) 2-(ethylamino)-ethanol was added. The reaction was allowed tocontinue for 24 hours at reflux. 0.7 g sodium iodide was added and thereaction was allowed to continue for another 24 hours at reflux. Theprecipitated salts were removed by filtration and the solvent wasremoved under reduced pressure. The residue was dissolved in 150 mLt.butyl methyl ether and extracted 4 times with 100 mL 0.1 Nhydrochloric acid. The aqueous fractions were pooled and the pH wasadjusted to 12, using a 5 N NaOH solution. The mixture was extractedwith 200 mL t.butyl methyl ether. The organic fraction was dried overMgSO₄ and evaporated under reduced pressure. 7.6 g (82%) of theintermediate was isolated.

7.6 g (21 mmol) of the intermediate thioxanthone was dissolved in 80 mLmethylene chloride. 2 mL (21 mmol) triethyl amine was added followed bythe drop wise addition of 2 mL (21 mmol) of 3-chloropropionyl chloride,while the temperature was kept below 35° C. The reaction was allowed tocontinue for one hour at room temperature. 0.5 g BHT was added to themixture followed by the addition of 5.8 mL (42 mmol) triethyl amine. Thereaction was allowed to continue for one hour at room temperature. 200mL ethyl acetate was added and the mixture was extracted twice with 100mL water. The organic fraction was dried over MgSO₄ and the solvent wasevaporated under reduced pressure. The crude INI-12 was purified bypreparative column chromatography on a Merck SVP D40 column, using agradient elution from 100% methylene chloride to methylenechloride/methanol 98/2 at a flow rate of 50 mL per minute. 5.94 g (69%)of INI-12 was isolated as a yellow oil.

The synthesis of INI-13:

5.1 g (17 mmol) 2-(3-chloropropoxy)-9H-thioxanthen-9-one was dissolvedin 80 mL acetonitrile. The mixture was heated to reflux and 8 mL (84mmol) 3-(methylamino)-1-propanol was added. The reaction was allowed tocontinue for 24 hours at reflux. 0.35 g sodium iodide was added and thereaction was allowed to continue for an additional 24 hours at reflux.The precipitated salts were removed by filtration and the solvent wasevaporated under reduced pressure. The residue was dissolved in 150 mLt.butyl methyl ether and extracted once with 300 mL 0.1 N hydrochloricacid and once with 150 mL 0.1 N hydrochloric acid. The aqueous fractionwas pooled and the pH was adjusted to 12 using 5 N NaOH. The mixture wasextracted with 200 mL t.butyl methyl ether. The organic fraction wasdried over MgSO₄ and the solvent was evaporated under reduced pressure.The crude intermediate was used without further purification.

The crude intermediate was dissolved in 80 mL methylene chloride. 2.8 mL(20 mmol) triethyl amine was added, followed by the drop wise additionof 2 mL (20 mmol) 3-chloropropionyl chloride, while the temperature waskept below 35° C. The reaction was allowed to continue for 1 hour atroom temperature. 0.5 g BHT was added, followed by the addition of 5.6mL (40 mmol) triethyl amine. The reaction was allowed to continue for 1hour at room temperature. 200 mL ethyl acetate was added and the mixturewas extracted twice with 100 mL water. The organic fraction was driedover MgSO₄ and evaporated under reduced pressure. The crude INI-13 waspurified by preparative column chromatography on a Merck SVP D40 column,using a gradient elution from 100% methylene chloride to methylenechloride/methanol 96/6 at a flow rate of 50 mL per minute. 4.64 g (66%)of INI-13 was isolated as a yellow oil.

Example 2

This example illustrates the influence of the polymerizable Norrishtype-II initiators according to a preferred embodiment of the presentinvention on the amount of volatile components desorbed from the layer,expressed as the TDE-level.

Preparation of Radiation Curable Compositions

The inventive radiation curable compositions INV- and INV-2 andcomparative curable composition COMP-1 were prepared according to Table5. The weight % (wt %) was based on the total weight of the radiationcurable composition.

TABLE 5 wt % of INV-1 INV-2 COMP-1 VEEA 67.0 62.0 74.5 Miramer M600 20.020.0 20.0 INI-5 10.0 15.0 — IRGACURE 127 — — 2.5 Surfactant A  3.0  3.03.0Preparation of Coated Samples

The free radical curable liquids COMP-1, INV-1 and INV-2 were coated ona PET100 substrate using a bar coater and a 10 mm wired bar. Each coatedsample was cured using a Fusion DRSE-120 conveyer, equipped with aFusion VPS/1600 lamp (D-bulb), which transported the samples twice underthe UV-lamp on a conveyer belt at a speed of 10 m/min.

To cure under nitrogen inerting conditions, the coated sample wasmounted on a metal plate and on top of the plate a metal frame of 1 cmheight with a non UV-absorbing quartz glass window was placed, so that asealed chamber was formed with the coated sample inside. Then, thetrapped air in the chamber was replaced by nitrogen gas by introducingpure nitrogen gas into the chamber for 30 seconds and the coated samplewas placed on the conveyer belt.

The curing degree was determined for the free radical curable liquidsCOMP-1, INV-1 and INV-2. The results are summarized in Table 6.

TABLE 6 Radiation curable Curing Curing composition under air under N₂INV-1 Fully cured Fully cured INV-2 Fully cured Fully cured COMP-1 Notcured Fully cured

The samples cured under nitrogen inerting conditions were used todetermine the TDE-level. The results for the free radical curableliquids COMP-1, INV-1 and INV-2 are summarized in Table 7. Coupling ofthe GC with mass spectroscopy revealed that none of the volatileresidues were related to the initiators according to preferredembodiments the present invention.

TABLE 7 Radiation curable TDE-level composition (ppm) INV-1 1085 INV-2970 COMP-1 510

From the results in Table 6 and Table 7, it can be concluded that thepolymerizable Norrish type-II initiators according to preferredembodiments the present invention result in a high curing speed over abroad range of curing circumstances, while still maintaining a low levelof volatile residues.

Example 3

This example illustrates that polymerizable Norrish type-II initiatorsaccording to a preferred embodiment of the present invention aresuitable to formulate pigmented radiation curable inkjet inks which arecurable both under air and under nitrogen.

Preparation of Radiation Curable Compositions

The inventive radiation curable compositions INV-3 to INV-6 wereprepared according to Table 8. The weight % (wt %) was based on thetotal weight of the radiation curable ink.

TABLE 8 wt % of INV-3 INV-4 INV-5 INV-6 VEEA 49.8 47.0 52.0 52.0 MiramerM600 20.0 20.0 20.0 20.0 Surfactant A  3.0  3.0  3.0  3.0 Disp K 17.2 —— — Disp M — 20.0 — — Disp Y — — 15.0 — Disp C — — — 15.0 INI-5 10.010.0 10.0 10.0

The pigment dispersions Disp K, Disp M, Disp Y and Disp C were preparedin the following manner.

Disp K

A concentrated pigment dispersion Disp K was made by mixing 466.7 g of a30 wt % solution of the polymeric dispersant in 535000 in DPGDA, 86.3 gof DPGDA, 7.0 g of the stabilizer GENORAD™ 16, 102.9 g of Special Black550 and 37.1 g of HOSTAPERM™ Blue P-BFS for 30 minutes using aDISPERLUX™ YELLOWO75 (from DISPERLUX S.A.R.L., Luxembourg) andsubsequently milling this mixture in a Eiger Lab Bead mill (from EIGERTORRANCE Ltd.) using yttrium-stabilized zirconium oxide-beads of 0.4 mmdiameter (“high wear resistant zirconia grinding media” from TOSOH Co.).The bead mill is filled for 52% with the grinding beads and water-cooledduring milling at 4250 rpm for 90 minutes. After milling the dispersionwas separated from the beads using a filter cloth. The concentratedpigment dispersion Disp K had an average particles size of 111 nmmeasured with a MALVERN™ nano-S particle size analyzer and a viscosityof 81 mPa·s at 10 s⁻¹ at 25° C.

Disp M

A concentrated pigment dispersion Disp M was made by mixing 466.7 g of a30 wt % solution of the polymeric dispersant in 535000 in VEEA, 86.3 gof VEEA, 7.0 g of the stabilizer GENORAD™ 16 and 140.0 g of CINQUASIA™Magenta RT-355-D for 30 minutes using a DISPERLUX™ YELLOWO75 (fromDISPERLUX S.A.R.L., Luxembourg) and subsequently milling this mixture ina Eiger Lab Bead mill (from EIGER TORRANCE Ltd.) usingyttrium-stabilized zirconium oxide-beads of 0.4 mm diameter (“high wearresistant zirconia grinding media” from TOSOH Co.). The bead mill isfilled for 52% with the grinding beads and water-cooled during millingat 4250 rpm for 220 minutes. After milling the dispersion was separatedfrom the beads using a filter cloth. The concentrated pigment dispersionDisp M had an average particles size of 96 nm measured with a MALVERN™nano-S particle size analyzer and a viscosity of 306 mPa·s at 10 s⁻¹ at25° C.

Disp Y

A concentrated pigment dispersion Disp Y was made by mixing 466.7 g of a30 wt % solution of the polymeric dispersant in 535000 in VEEA, 86.3 gof VEEA, 7.0 g of the stabilizer GENORAD™ 16 and 140.0 g of PY150 for 30minutes using a DISPERLUX™ YELLOWO75 (from DISPERLUX S.A.R.L.,Luxembourg) and subsequently milling this mixture in a Eiger Lab Beadmill (from EIGER TORRANCE Ltd.) using yttrium-stabilized zirconiumoxide-beads of 0.4 mm diameter (“high wear resistant zirconia grindingmedia” from TOSOH Co.). The bead mill is filled for 52% with thegrinding beads and water-cooled during milling at 4250 rpm for 220minutes. After milling the dispersion was separated from the beads usinga filter cloth. The concentrated pigment dispersion Disp Y had anaverage particles size of 136 nm measured with a MALVERN™ nano-Sparticle size analyzer and a viscosity of 275 mPa·s at 10 s⁻¹ at 25° C.

Disp C

A concentrated pigment dispersion Disp C was made by mixing 466.7 g of a30 wt % solution of the polymeric dispersant in 535000 in VEEA, 86.3 gof VEEA, 7.0 g of the stabilizer GENORAD™ 16 and 140.0 g of HOSTAPERM™Blue P-BFS for 30 minutes using a DISPERLUX™ YELLOWO75 (from DISPERLUXS.A.R.L., Luxembourg) and subsequently milling this mixture in a EigerLab Bead mill (from EIGER TORRANCE Ltd.) using yttrium-stabilizedzirconium oxide-beads of 0.4 mm diameter (“high wear resistant zirconiagrinding media” from TOSOH Co.). The bead mill is filled for 52% withthe grinding beads and water-cooled during milling at 4250 rpm for 220minutes. After milling the dispersion was separated from the beads usinga filter cloth. The concentrated pigment dispersion Disp Y had anaverage particles size of 113 nm measured with a MALVERN™ nano-Sparticle size analyzer and a viscosity of 129 mPa·s at 10 s⁻¹ at 25° C.

Preparation of Coated Samples

The free radical curable liquids INV-14 to INV-21 were coated on aPET100 substrate using a bar coater and a 10 mm wired bar. Each coatedsample was cured using a Fusion DRSE-120 conveyer, equipped with aFusion VPS/1600 lamp (D-bulb), which transported the samples twice underthe UV-lamp on a conveyer belt at a speed of 10 m/min.

To cure under nitrogen inerting conditions, the coated sample wasmounted on a metal plate and on top of the plate a metal frame of 1 cmheight with a non UV-absorbing quartz glass window was placed, so that asealed chamber was formed with the coated sample inside. Then, thetrapped air in the chamber was replaced by nitrogen gas by introducingpure nitrogen gas into the chamber for 30 seconds and the coated samplewas placed on the conveyer belt.

The curing degree and the viscosity were determined for the free radicalcurable inks INV-3 to INV-6 and are summarized in Table 9.

TABLE 9 Radiation Viscosity Curing Curing curable ink (mPa · s) underair under N₂ INV-3 16 Fully cured Fully cured INV-4 25 Fully cured Fullycured INV-5 20 Fully cured Fully cured INV-6 11 Fully cured Fully cured

From Table 9, it becomes clear that all the radiation curable inks curewell both under air and under nitrogen and are well within the viscosityrange to be jettable.

Example 4

This example illustrates the importance of the design in the linkinggroup L of the polymerizable Type II photoinitiators according to apreferred embodiment of the present invention.

Preparation of Radiation Curable Compositions

The inventive radiation curable compositions INV-7 to INV-11 andcomparative curable compositions COMP-2 and COMP-3 were preparedaccording to Table 10. The weight % (wt %) was based on the total weightof the radiation curable composition.

TABLE 10 wt % of INV-7 INV-8 INV-9 INV-10 INV-11 COMP-2 COMP-3 DPGDA40.5 39.5 38.5 43.5 42.5 36.0 47.0 TMPTA 40.0 40.0 40.0 40.0 40.0 40.040.0 INI-2 17.5 — — — — — — INI-3 — 18.5 — — — — — INI-4 — — 19.5 — — —— INI-9 — — — 14.5 — — — INI-13 — — — — 15.5 — — COMPINI-1 — — — — — —11.0 COMPINI-2 — — — — — 12.0 — COMPCOINI-1 — — — — — 10.0 — Dibutyl 2.0  2.0  2.0  2.0  2.0  2.0  2.0 phthalate

Dibutyl phthalate was added to the radiation curable compositions sothat it could be used as an internal reference for the analysis ofextractable residues.

Preparation of Coated Samples

The free radical curable liquids COMP-2 and 3 and INV-7 to INV-11 werecoated on a PET100 substrate using a bar coater and a 10 mm wired bar.Each coated sample was cured using a Fusion DRSE-120 conveyer, equippedwith a Fusion VPS/1600 lamp (D-bulb), which transported the samplesunder the UV-lamp on a conveyer belt at a speed of 20 m/min.

To cure under nitrogen inerting conditions, the coated sample wasmounted on a metal plate and on top of the plate a metal frame of 1 cmheight with a non UV-absorbing quartz glass window was placed, so that asealed chamber was formed with the coated sample inside. Then, thetrapped air in the chamber was replaced by nitrogen gas by introducingpure nitrogen gas into the chamber for 30 seconds and the coated samplewas placed on the conveyer belt.

The curing speed was determined for radiation curable compositionsCOMP-2 and 3 and INV-7 to INV-11. The results are summarized in Table11.

TABLE 11 Radiation curable Curing under Curing under composition air 20m/min N₂ 20 m/min INV-7 Fully cured Fully cured INV-8 Fully cured Fullycured INV-9 Fully cured Fully cured INV-10 Fully cured Fully curedINV-11 Fully cured Fully cured COMP-2 Fully cured Fully cured COMP-3Fully cured Fully cured

From Table 11, it can be concluded that all curable compositions, bothcomparative and inventive, cure well enough both under air and undernitrogen to determine extractable residues.

The Extraction Procedure:

Two samples of 7.068 cm² of COMP-2 and 3 and INV-7 to INV-11 were putinto a 50 mL beaker and extracted with 4.5 mL acetonitrile, usingultrasound for 30 minutes. The extract was transferred into a 5 mLvolumetric flask. The samples were rinsed twice with a small amount ofacetonitrile and the rinsing solvent was transferred into the 5 mLvolumetric flask until the volume was adjusted to 5 mL. The solution wasthoroughly mixed and filtered over a 0.45 mm filter. 10 mL of eachsample was injected on the HPLC.

The Chromatographic Method:

An Alltima C18 5 mm column (150×3.2 mm), supplied by Alltech, was used.A flow rate of 0.5 mL/min was used at a temperature of 40° C. A DADdetector at 291 nm was used to detect the extracted initiator andinitiator fragments.

The following HPLC-method was used for all samples.

-   -   Eluent A: H₂O+0.02M KH₂PO₄ pH=2.5 using H₃PO₄    -   Eluent B: H₂O+0.02M KH₂PO₄ pH=2.5 using H₃PO₄/CH₃CN [40/60]        (v/v)    -   Eluent C: H₂O/CH₃CN [40/60] (v/v)    -   Eluent D: H₂O/CH₃CN [10/90] (v/v)

Gradient (end run=38 min)

TABLE 12 Time % eluent % eluent % eluent % eluent (min) A B C D 0 70 300 0 6 70 30 0 0 11 0 100 0 0 20 0 100 0 0 21 0 0 100 0 24 0 0 100 0 25 00 0 100 30 0 0 0 100 31 70 30 0 0 38 70 30 0 0

Assumptions made to calculate the amount of extractable residues:

In each sample, all peaks, showing the same UV-VIS-spectrum as thereference benzophenone comparative initiator 2, were integrated to takepotential degradation products from the different initiators, whichbecome extractable, into account.

To calculate the amount of extractable residues, expressed as mg/m², itwas assumed that the average molecular weight of all compounds takeninto account remained unchanged, compared to the original initiator,which for the polymeric initiators probably leads to an overestimationof the extractable residues.

The concentration was determined in comparison with a reference sampleof a known concentration of each comparative and inventive initiator,eluted under the same conditions as the extracted samples.

A total coating weight of 10 g/m² was assumed for each sample.

The results are summarized in Table 13. The wt % of extracted initiatoris based on the total wt % of the initiator of the original radiationcurable composition. The comparative co-initiator COMPCOINI-1 in COMP-2is not detectable under these chromatographic conditions.

TABLE 13 Radiation curable Extractable wt % of extracted compositionresidues (mg/m²) initiator INV-7 162 9 INV-8 145 8 INV-9 270 14 INV-1089 6 INV-11 37 2 COMP-2 885 74 COMP-3 440 40

From Table 13, one can see that the extraction of the polymerizable TypeII photoinitiator is strongly reduced.

Example 5

This example illustrates that the polymerizable Type II photoinitiatorsaccording to a preferred embodiment of the present invention exhibithigh curing speed even in the absence of a co-initiator, as well as lowextractables.

Preparation of Radiation Curable Compositions

The inventive radiation curable compositions INV-12 to INV-15 andcomparative curable compositions COMP-4 and COMP-5 were preparedaccording to Table 14. The weight % (wt %) was based on the total weightof the radiation curable composition.

TABLE 14 wt % of INV-12 INV-13 INV-14 INV-15 COMP-4 COMP-5 DPGDA 40.043.5 42.5 39.5 — — TMPTA 40.0 40.0 40.0 40.0 40.0 40.0 INI-6 18.0 — — —— — INI-12 — 14.5 — — — — INI-10 — — 15.5 — — INI-7 — — — 18.5 — —COMPINI-1 — — — — — 11.0 COMPINI-2 — — — — 12.0 — COMPCOINI-2 — — — —10.0 — Dibutyl phthalate  2.0  2.0  2.0  2.0  2.0  2.0Preparation of Coated Samples

The free radical curable liquids COMP-4, COMP-5 and INV-12 to INV-15were coated on a PET100 substrate using a bar coater and a 10 mm wiredbar. Each coated sample was cured using a Fusion DRSE-120 conveyer,equipped with a Fusion VPS/1600 lamp (D-bulb), which transported thesamples under the UV-lamp on a conveyer belt at a speed of 10 m/min,when cured under air and at 20 m/min when cured under nitrogen.

To cure under nitrogen inerting conditions, the coated sample wasmounted on a metal plate and on top of the plate a metal frame of 1 cmheight with a non UV-absorbing quartz glass window was placed, so that asealed chamber was formed with the coated sample inside. Then, thetrapped air in the chamber was replaced by nitrogen gas by introducingpure nitrogen gas into the chamber for 30 seconds and the coated samplewas placed on the conveyer belt.

The curing degree and the viscosity were determined for the free radicalcurable compositions COMP-4, COMP-5 and INV-12 to INV-15 and aresummarized in Table 15.

TABLE 15 Radiation curable Curing under Curing under composition air 20m/min N₂ 20 m/min INV-12 Fully cured Fully cured INV-13 Fully curedFully cured INV-14 Fully cured Fully cured INV-15 Fully cured Fullycured COMP-4 Fully cured Fully cured COMP-5 Fully cured Fully cured

From Table 15, it can be concluded that all curable compositions, bothcomparative and inventive, cure well enough both under air and undernitrogen to determine extractable residues.

The Extraction Procedure and Chromatographic Method

The same extraction procedure and chromatographic method as described inEXAMPLE 4 was used on two samples of 7.068 cm² of INV-12 to INV-15 andCOMP-4 and COMP-5.

Assumptions made to calculate the amount of extractable residues:

-   -   For INV-12, where a mixtures of thioxanthones was used, all        peaks showing the same UV-VIS-spectrum as the model thioxanthone        MTX1, given below, were integrated to take potential degradation        products from the different initiators, which become        extractable, into account In INV-13 to INV-15, pure        benzophenones and thioxanthones were used.

-   -   The extractable residues of the exact compounds were determined.        Where a mixture of initiators was used, it was assumed that the        average molecular weight of all compounds taken into account        remained unchanged, compared to the original initiator, to        calculate the amount of extractable residues, expressed as        mg/m².    -   The concentration was determined in comparison with a reference        sample of a known concentration of each comparative and        inventive initiator, eluted under the same conditions as the        extracted samples.    -   A total coating weight of 10 g/m² was assumed for each sample.

The results are summarized in Table 17. The wt % of extracted initiatoris based on the total wt % of the initiator of the original radiationcurable composition. The extracted amount of comparative co-initiatorCOMPCOINI-2 for COMP-4 is given between brackets.

TABLE 17 Radiation curable Extractable % of the initiator, compositionresidues (mg/m²) which remains extractable INV-12 74 4 INV-13 4 <1INV-14 59 4 INV-15 128 7 COMP-4 1059 (425) 88 COMP-5 440 40

From Table 17, it becomes clear that the initiators, according topreferred embodiments of the present invention, significantly reduce theamount of extractable residues.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing the scope andspirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

1. A polymerizable Type II photoinitiator according to Formula (I):

wherein: A represents a Norrish Type II initiating group; L represents adivalent linking group positioning the Norrish Type II initiating groupA and the CR2R3-group in a 1-5 to a 1-8 position wherein position 1 isdefined as the first atom in the aromatic or alicyclic ring of A towhich L is covalently bonded and the position 5 to 8 is defined as thecarbon atom of the CR2R3-group to which L is covalently bonded, with theproviso that L does not contain an amine; R1 represents an optionallysubstituted group selected from the group consisting of an alkyl group,an alkenyl group, an alkynyl group, an aralkyl group, an alkaryl group,an aryl group, and a heteroaryl group; R2 to R6 each independentlyrepresent a hydrogen or an optionally substituted group selected fromthe group consisting of an alkyl group, an alkenyl group, an alkynylgroup, an aralkyl group, an alkaryl group, an aryl group, and aheteroaryl group, with the proviso that at least one of R2 to R6represents a hydrogen; any two or three groups of the group selectedfrom R1 to R6 and L may represent the necessary atoms to form a five toeight membered ring; and with the proviso that at least one of L, R1 toR6, and A is substituted with at least one ethylenically unsaturatedpolymerizable group selected from the group consisting of an acrylategroup, a methacrylate group, an acrylamide group, a methacrylamidegroup, a styrene group, a vinyl ether group, an allyl ether group, anallyl ester group, a vinyl ester group, a succinate group, a maleategroup, and a maleimide group.
 2. A polymerizable Type II photoinitiatoraccording to Formula (I): wherein: A represents a Norrish Type IIinitiating group; L represents a divalent linking group positioning theNorrish Type II initiating group A and the CR2R3-group in a 1-5 to a 1-8position wherein position 1 is defined as the first atom in the aromaticor alicyclic ring of A to which L is covalently bonded and the position5 to 8 is defined as the carbon atom of the CR2R3-group to which L iscovalently bonded, with the proviso that L does not contain an amine; R1represents an optionally substituted group selected from the groupconsisting of an alkyl group, an alkenyl group, an alkynyl group, anaralkyl group, an alkaryl group, an aryl group, and a heteroaryl group;R2 to R6 each independently represent a hydrogen or an optionallysubstituted group selected from the group consisting of an alkyl group,an alkenyl group, an alkynyl group, an aralkyl group, an alkaryl group,an aryl group, and a heteroaryl group, with the proviso that at leastone of R2 to R6 represents a hydrogen; any two or three groups of thegroup selected from R1 to R6 and L may represent the necessary atoms toform a five to eight membered ring; and with the proviso that at leastone of L, R1 to R6, and A is substituted with at least one ethylenicallyunsaturated polymerizable group according to Formula (II):

wherein X represents a functional group selected from the groupconsisting of OR7, S(O)_(n)R8, and NR9R10; Y represents a functionalgroup selected from the group consisting of OR11 and NR12R13; R8 to R10represent an optionally substituted group selected from the groupconsisting of an alkyl group, an alkenyl group, an alkynyl group, anaralkyl group, an alkaryl group, an aryl group, and a heteroaryl group;R7 and R11 to R13 represent a hydrogen or an optionally substitutedgroup selected from the group consisting of an alkyl group, an alkenylgroup, an alkynyl group, an aralkyl group, an alkaryl group, an arylgroup, and a heteroaryl group; and R9 and R10 and R12 and R13 mayrepresent the necessary atoms to form a five to eight membered ring. 3.The polymerizable Type II photoinitiator according to claim 1, whereinthe Norrish Type II initiating group A is selected from the groupconsisting of a substituted or unsubstituted benzophenone and asubstituted or unsubstituted thioxanthone.
 4. The polymerizable Type IIphotoinitiator according to claim 1, wherein R1 is selected from thegroup consisting of a substituted or unsubstituted alkyl group and asubstituted or unsubstituted aryl group.
 5. The polymerizable Type IIphotoinitiator according to claim 4, wherein R1 represents an aryl groupaccording to Formula (III):

wherein the dotted line represents a chemical bond to the nitrogen atomin Formula (I) and E represents a group selected from the groupconsisting of an ester, an aldehyde, a ketone, and an amide.
 6. Thepolymerizable Type II photoinitiator according to claim 5, wherein thegroup E represents an ester group.
 7. A polymerizable Type IIphotoinitiator according to Formula (I):

wherein: A represents a Norrish Type II initiating group; L represents adivalent linking group represented by the group —O—(CH2)n— with nrepresenting an integer having a value of 3; R1 represents an optionallysubstituted group selected from the group consisting of an alkyl group,an alkenyl group, an alkynyl group, an aralkyl group, an alkaryl group,an aryl group, and a heteroaryl group; R2 to R6 each independentlyrepresent a hydrogen or an optionally substituted group selected fromthe group consisting of an alkyl group, an alkenyl group, an alkynylgroup, an aralkyl group, an alkaryl group, an aryl group, and aheteroaryl group, with the proviso that at least one of R2 to R6represents a hydrogen; any two or three groups of the group selectedfrom R1 to R6 and L may represent the necessary atoms to form a five toeight membered ring; and with the proviso that at least one of L, R1 toR6, and A is substituted with at least one ethylenically unsaturatedpolymerizable group selected from the group consisting of an acrylategroup, a methacrylate group, an acrylamide group, a methacrylamidegroup, a styrene group, a vinyl ether group, an allyl ether group, anallyl ester group, a vinyl ester group, a succinate group, a maleategroup, and a maleimide group.
 8. A radiation curable compositioncomprising: the polymerizable Type II photoinitiator according toclaim
 1. 9. The radiation curable composition according to claim 8,wherein the composition includes a colorant.
 10. The radiation curablecomposition according to claim 8, wherein the radiation curablecomposition is a radiation curable inkjet ink.
 11. A radiation curableink set comprising: at least two of the radiation curable compositionsaccording to claim
 8. 12. An inkjet printing method comprising the stepsof: providing the radiation curable composition according to claim 8;and at least partially curing the radiation curable composition.
 13. Theinkjet printing method according to claim 12, further comprising thesteps of: applying the radiation curable composition to a substrate byflexographic printing; and printing an inkjet ink upon the at leastpartially cured radiation curable composition.
 14. The inkjet printingmethod according to claim 12, further comprising the step of: jettingthe radiation curable composition upon a substrate.
 15. Thepolymerizable Type II photoinitiator according to claim 1, wherein theat least one ethylenically unsaturated polymerizable group is anacrylate group.
 16. The polymerizable Type II photoinitiator accordingto claim 3, wherein the at least one ethylenically unsaturatedpolymerizable group is an acrylate group.
 17. The polymerizable Type IIphotoinitiator according to claim 5, wherein the at least oneethylenically unsaturated polymerizable group is an acrylate group. 18.The polymerizable Type II photoinitiator according to claim 7, whereinthe at least one ethylenically unsaturated polymerizable group is anacrylate group.